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  Java Practices -> Use standard Collections
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<div class='page-title'>Use standard Collections</div>

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<br>In the <a href="http://java.sun.com/javase/6/docs/technotes/guides/collections/index.html">Collections Framework</a>, there are many implementation classes
to choose from. Most of the time, one of these "primary implementations"
is the appropriate choice
<ul>
<li>
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ArrayList.html">ArrayList</a></tt>,
for an implementation of the <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/List.html">List</a></tt>
interface</li>

<li>
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/LinkedHashMap.html">LinkedHashMap</a></tt>, 
for an implementation of the <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Map.html">Map</a></tt>
interface</li>

<li>
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/LinkedHashSet.html">LinkedHashSet</a></tt>, 
for an implementation of the <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Set.html">Set</a></tt>
interface</li>

<li>
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/ArrayDeque.html">ArrayDeque</a></tt>, 
for an implementation of both the the <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Deque.html">Deque</a></tt>
and 
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/Queue.html">Queue</a></tt>
interfaces</li>
</ul>

<P>Before JDK 1.5, 
<a href="http://java.sun.com/javase/6/docs/api/java/util/HashMap.html"><tt>HashMap</tt></a> and 
<a href="http://java.sun.com/javase/6/docs/api/java/util/HashSet.html"><tt>HashSet</tt></a> 
were the preferred implementations of 
<tt>Map</tt> and <tt>Set</tt>. However, the iterators returned by those classes have 
the somewhat bizarre property of having an <em>undefined</em> order. That is, iterating over 
a <tt>HashMap</tt> or <tt>HashSet</tt>
can return elements in a different order at different times. Their iteration order is not guaranteed to be 
repeatable (and often isn't). 
Even though <tt>HashMap</tt> and <tt>HashSet</tt> have 
slightly better overall performance, for most business applications it is likely best to avoid such 
undefined behavior.

<p>To retain the sorting of items being manipulated in a graphical user
interface,
<tt><a href="http://java.sun.com/javase/6/docs/api/java/util/TreeSet.html">TreeSet</a></tt>
and <tt><a href="http://java.sun.com/javase/6/docs/api/java/util/TreeMap.html">TreeMap</a></tt>
are useful. They force a collection to maintain a sort order when the user
adds and deletes items.
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<div class='topic-section'>See Also :</div>
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  <a href='TopicActionc6f5-2.html?Id=65'>Choosing the right Collection</a> <br>
 
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